This invention relates to a suspension system and more particularly to a vehicle suspension utilizing a torsion spring in cooperation with a leaf spring suspension.
It is conventional to use a leaf spring at each side of the vehicle to provide the suspension means between the frame of the vehicle and the axle, such that one end of the leaf spring is pivotally fixed to the frame and the other end connected via a shackle to the frame. In many instances such as in pick-up trucks as well as large trucks, the suspension means is designed to give acceptable rides where the vehicle is substantially loaded but provide a poor and uncomfortably stiff ride when the vehicle is very lightly loaded as with only the driver and possibly a passenger with no cargo. In some instances, this condition exists because the rear springs are designed for rated (full cargo) loads and such springs are far too stiff. In addition to the above, helper springs are also used in conjunction with the leaf spring but this only aggravates the problem.
The present invention is directed to a double link system employing a double-link torsion spring in series with a leaf spring wherein the torsion spring acts initially as the sole means for providing the suspension means giving a very comfortable ride under lightly loaded conditions. Such series connection of the torsion spring to the leaf spring dampens road noise that is normally transmitted through the ordinary shackle. As the load approaches the rated load value (cargo added), the double-link torsion spring locks up and the leaf spring takes up the full load providing the desired designed ride. Of importance in the above described suspension systems is that the leaf spring system itself exhibits a lower spring rate (softer) when the torsion spring which is in series with the leaf spring is not locked out.